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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: b1llso on November 19, 2016, 12:40:07 PM

Title: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: b1llso on November 19, 2016, 12:40:07 PM: (https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimgur.com%2FdbOCZCm&hash=30a04efd3890638e41422f5e282b6256a2265150)

How would this mechanism work? I know that first step produces sodium phenoxide and hydrogen gas, but after that I'm pretty much lost. *delete me*
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: AWK on November 19, 2016, 01:52:56 PM: Search textbook for synthsis of ethers.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: Babcock_Hall on November 19, 2016, 03:02:10 PM: Think about nucleophiles and leaving groups.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: rolnor on November 20, 2016, 03:04:55 PM: Is not 1-bromopropene a vinyl halide and not very reactive against nucleophiles? 3-bromopropene would react off course.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: AWK on November 20, 2016, 03:20:18 PM: I treated this compound as 3-bromopropene, since reaction is expected.
b1llso, please confirm structure or simply draw it using smiles
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: rolnor on November 21, 2016, 01:54:28 PM: I think if you want the vinylether one can use copper phenolates, sorry though, I dont remember the reference. I dont understand why one would choose sodium metal as the base, sodium hydride or sodium methoxide is more common?
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: wildfyr on November 27, 2016, 08:37:11 PM: Allyl bromide actually reacts kind of funny I think. I believe it reacts thusly (known as SN2 prime?):

P.S. I dont get why you need sodium to do this reaction. shouldnt it work with some nice acid scavenger like TEA?
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: rolnor on November 28, 2016, 07:46:46 AM: You need stronger base to get the phenolate. Triethylamine is itself a nucleophile also.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: wildfyr on November 28, 2016, 05:56:05 PM: TEA is a pretty terrible nucleophile. You can quaternize it by heating the f&#$ out of it, or using a trick like AgNO3 to push it forward, but the phenol will outcompete it under basic conditions. You don't need a formal phenolate to get nucleophilic attack, you just need a base scavanger.

What my basic question is, why not run this as boring old aryl williamson ether? I think K2CO3 is a typical base for that, though I dont see why TEA wouldnt work just fine. Sodium to get a phenolate just seems extreme here when allyl bromide is a kickass electrophile. What the heck, you could even use KOH if you want the phenolate so badly if you add it before the ally bromide.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: rolnor on November 29, 2016, 07:51:03 AM: I dont agree, triethylamine and a phenol is about as bad nucleophiles equaly. K2CO3 or NaH would be better as base.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: wildfyr on November 29, 2016, 08:23:54 PM: You dont think if you put TEA and phenol together you would get mostly phenolate and protonated amine?
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: Dan on November 30, 2016, 05:30:27 AM: Quote from: wildfyr on November 29, 2016, 08:23:54 PM
You dont think if you put TEA and phenol together you would get mostly phenolate and protonated amine?

Depends on the solvent. In water the pKas of phenol and triethylammonium are 10 and 11 respectively (i.e. triethylammonium phenolate is favoured), but in DMSO (http://www.chem.wisc.edu/areas/reich/pkatable/) the pKas of phenol and triethylammonium are 18 and 9 respectively (i.e. very little phenolate formation).
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: rolnor on November 30, 2016, 10:31:11 AM: Quote from: Dan on November 30, 2016, 05:30:27 AM
Quote from: wildfyr on November 29, 2016, 08:23:54 PM
You dont think if you put TEA and phenol together you would get mostly phenolate and protonated amine?

Depends on the solvent. In water the pKas of phenol and triethylammonium are 10 and 11 respectively (i.e. triethylammonium phenolate is favoured), but in DMSO (http://www.chem.wisc.edu/areas/reich/pkatable/) the pKas of phenol and triethylammonium are 18 and 9 respectively (i.e. very little phenolate formation).
I am surprised that phenol is as strong acid so you are right, at least in water solution. Still, for mee, it feels more natural to use carbonate or hydride as base.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: wildfyr on December 01, 2016, 07:07:16 PM: I agree. It really hadnt occured to me to check the DMSO (or MeCN) pkas. carbonate, (quantitative) hydroxide, or hydride would work best.
Title: Re: 2 step phenol reaction with metallic sodium and 1-bromo-propene
Post by: rolnor on December 01, 2016, 07:35:39 PM: I give you a Molsnack+ wildfyr :)